Semiconductor devices incorporating P-type and N-type impurity induced layer disordered material

ABSTRACT

Novel semiconductor devices are monolithically defined with p-type and n-type wide bandgap material formed by impurity induced layer disordering of selected regions of multiple semiconductor layers. The devices are beneficially fabricated by simultaneously forming the n-type and p-type layer disordered regions with sufficiently abrupt transitions from disordered to as-grown material. The novel devices include a heterojunction bipolar transistor monolithically integrated with an edge emitting heterostructure laser or a surface emitting laser, a heterostructure surface emitting laser, a heterostructure surface emitting laser having active distributed feedback, devices containing multiple buried layers which are individually contacted such as p-n junction surface emitting lasers, carrier channeling devices, and &#34;n-i-p-i&#34; or hetero &#34;n-i-p-i&#34; devices, and novel interdigitated structures, such as optical detectors and distributed feedback lasers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel semiconductor devices and structureswhich incorporate p-type and n-type wide bandgap material formed byimpurity induced layer disordering of multiple semiconductor layers.U.S. Pat. No. 5,376,583, issued Dec. 24, 1994, describes a method formaking p-type doped materials alone or simultaneously with n-typedisordered materials and is incorporated herein by reference.

In particular, this invention relates to five overlapping classes ofnovel devices: integrated transistor and edge emitting laser diodes;integrated transistors and surface emitting diodes; a laterally injectedsurface emitting laser diode; a carrier channeling or "nipi" device; andan interdigitated semiconductor device. Further, the laterally injectedsurface emitting laser diodes includes devices having active distributedoptical feedback to achieve lasing oscillation. These active distributeddevices may incorporate only one or both of the n-type and p-type IILDmaterials.

2. Related Art

Impurity-induced layer disordering of multiple layers of Group III-Vcompound semiconductors is an important step in fabricatingoptoelectronic devices such as lasers, transistors, and photodiodes. Thediffusion of silicon or the like into multiple layers of Group III-Vsemiconductors under Group V-rich conditions is well known to form layerdisordered material. Unfortunately, such impurity induced layerdisordering with silicon was limited to forming n-type material. Inaddition, while it is known that-he diffusion of zinc into multiplelayers of Group III-V semiconductors forms p-type doped layer disorderedmaterial, such p-type semiconductor materials were not suitable for usein many devices because zinc diffused materials lack an abrupt andreproducible transition from the ordered to disordered material.

Accordingly, most known devices requiring both p-type and n-type dopedmaterials formed by impurity induced layer disordering could not beusefully manufactured.

In particular, surface emitting diode lasers are an important lightsource for many applications, such as optical disk systems, laserprinting and scanning, optical interconnections, and fiber opticcommunications. One problem with such lasers is that they inherentlyhave much less available optical gain than edge-emitting lasers, due tothe small active volume of the surface emitter. Consequently, achievinga useful level of performance requires efficient use of the availableoptical gain and minimizing both the optical loss and heat generated inthe surface emitting structure.

A partial solution to the gain problem is disclosed by S. W. Corzine, etal., in "Design of Fabry-Perot Surface-Emitting Lasers with a PeriodicGain Structure", IEEE Journal of Quantum Electronics Vol. 25(6), pp.1513-1524, June 1989. Corzine teaches periodically spacing the activelayers between the mirrors of the surface emitting laser cavity. Theoptimum spacing is chosen such that the active layer coincides with themaximum in the standing wave pattern of the optical field set up by thecavity mirrors. This spacing is approximately one-half of the lasingwavelength in the semiconductor.

Although such periodic gain enables more efficient use of the opticalgain than a uniformly excited active layer, this approach has severallimitations. For example, the threshold current increases as the bandgapof the passive layer between pairs of active layers is increased,thereby preventing the maximum confinement of charged carriers in theactive layer, which is needed for operation at high temperatures.Furthermore, Corzine teaches placement of the periodic gain regionwithin a laser cavity formed by two distributed Bragg reflectors, bothof which require at least 18 to 25 layers to achieve the required levelof reflectivity. Maximizing the electrical conductivity of these layersis not consistent with minimizing their optical absorption. Finally,Corzine fails to provide any means for electrically exciting the activelayers.

Another problem for surface emitting lasers is that achieving a usefullevel of performance requires minimizing optical loss in the surfaceemitting structure. Consequently, using undoped active and passivelayers throughout the construction of such lasers is desirable, in orderto avoid optical absorption from free carriers. However, undoped layershave poor electrical conductivity, which is not consistent with the lowelectrical resistance required to minimize the heat generated ininjection type diode lasers. This is especially a problem when theelectrical current must pass through 20, 30 or more layers in the gainregion and another 20 to 30 layers in each of the cavity mirrors.Excessive heating in the surface emitter not only increases thethreshold current, but most seriously shifts the lasing wavelength awayfrom the optimum wavelength of the cavity mirrors.

A partial solution to the optical loss/conductivity problem is disclosedby A. Scherer, et al., in "Fabrication of Low Threshold VoltageMicrolasers", Electronics Letters Vol. 28(13), pp. 1224-1226, June 1992.In Scherer's approach, current is injected through a thin heavily dopedcontact layer grown under the output mirror of the cavity, therebyavoiding the current having to pass through one undoped mirror. However,the current must still pass through the other cavity mirror, which ishighly doped for electrical conductivity and therefore introducessignificant optical loss. The current must also pass through the activelayers, which are undoped and are therefore electrically resistive.Therefore, it is impractical to combine the contacting approach ofScherer with the periodic gain teachings of Corzine. In addition,implementing Scherer's contact requires etching through the outputmirror to expose the underlying contact layer, thereby introducingundesirable manufacturing cost and complexity, as well as potentiallylowering the yield due to damage to the mirror.

Accordingly, there is need for designs and fabrication techniques whichenable low current, low voltage and high temperature operation ofsurface emitting diode lasers. Beneficially, those designs andfabrication techniques should be applicable to constructing arrays ofclosely spaced, independently addressable surface emitting lasers.

3. Related Application

In U.S. Pat. No. 5,376,583 novel methods are disclosed for producingp-type wide bandgap material by impurity induced layer disordering(IILD) of multiple semiconductor layers and for simultaneously producingn-type and p-type IILD materials in the same set of multiplesemiconductor layers.

SUMMARY OF THE INVENTION

This invention provides for novel optoelectronic devices comprising aheterojunction bipolar transistor monolithically integrated with aheterostructure laser, wherein all operational contacts are beneficiallyon one surface of the device.

This invention also provides for novel optoelectronic devices comprisinga heterostructure laser monolithically integrated with a heterojunctionbipolar transistor having a base contact on the substrate side of thechip.

This invention further provides for novel semiconductor devicescontaining multiple buried layers which individually contact either awide bandgap collector or emitter. The devices may require p-type,n-type, or p-type and n-type contacting. Structures of this type are p-njunction surface emitting lasers, carrier channeling devices, and"n-i-p-i" or hetero "n-i-p-i" devices.

This invention additionally provides for novel interdigitatedstructures. Structures of this type can be used, for example, to makefast optical detectors or distributed feedback lasers.

This invention also provides for a novel laterally injected surfaceemitting laser having the laser anode and cathode on the emittingsurface of the chip.

This invention additionally provides for a novel laterally injectedactive distributed feedback surface emitting laser having the lasercathode on the emitting surface of the chip and the laser anode on anopposite side of the chip.

This invention further provides for a novel laterally injected activedistributed feedback surface emitting laser having the laser anode onthe emitting surface of the chip and the laser cathode on an oppositeside of the chip.

It is a principal object of this invention to fabricate novelsemiconductor devices with selected regions of n-type and p-type widebandgap material formed by impurity induced layer disordering within amultiple layer semiconductor structure.

It is a further object of this invention to fabricate such novelsemiconductor devices by simultaneously forming said n-type and p-typelayer disordered regions.

It is another principal object of this invention to minimize the numberof layers required in a surface emitting laser structure by obtainingthe optical feedback required to sustain lasing oscillation from thestructure of the active layers providing the optical gain.

It is a further object of this invention to minimize the operatingvoltage in an electrically activated surface emitting laser structure byinjecting charge carriers directly into the active layers, therebyeliminating current passing through passive layers of the structure.

It is yet another object of this invention to provide a high densityarray of such surface emitting lasers on a single substrate.

According to this invention, the novel devices are formed within amultilayer semiconductor structure by impurity induced layer disorderingwhich selectively produces n-type and/or p-type wide bandgap material,wherein the transition from ordered layers to p-doped disordered layershas a sufficiently abrupt and reproducible transition.

According to this invention, the novel surface emitting lasers andarrays are formed within an optically active distributed feedbackmultilayer structure by impurity induced layer disordering to formn-type and/or p-type material.

Other devices and advantages, together with the full understanding ofthe invention, will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in relation to the following drawings, inwhich like reference symbols refer to like elements, and wherein:

FIG. 1 is a cross-sectional view of a monolithic N-P-N transistor andedge emitting laser formed with operational contacts on one surface;

FIG. 2 is a cross-sectional view of a monolithic edge emitting laser andP-N-P transistor formed with its base contact on the substrate side ofthe chip;

FIG. 3A is a top plan view of a monolithic N-P-N transistor and surfaceemitting laser formed with operational contacts on one surface;

FIG. 3B is a cross-sectional view of the integrated transistor/laser ofFIG. 3A;

FIG. 4A is a top plan view of a monolithic surface emitting laser andP-N-P transistor formed with its base contact on the substrate side ofthe chip;

FIG. 4B is a cross-sectional view of the integrated transistor/laser ofFIG. 4A;

FIG. 5A is a top plan view of a laterally injected surface emittinglaser having its anode and cathode on the emitting surface;

FIG. 5B is a cross-sectional view of the laterally injected surfaceemitting laser of FIG. 5A;

FIG. 6A is a top plan view of a laterally contacted carrier channelingor "nipi" device formed according to the principles of this invention;

FIG. 6B is a cross-sectional view of the laterally contacted carrierchanneling or nipi device of FIG. 6A;

FIG. 7 is a schematic diagram of the layer structure utilized in a"nipi" device;

FIG. 8A is a top plan view of an interdigitated semiconductor deviceformed according to the principles of this invention;

FIG. 8B is a cross-sectional view of the semiconductor device of FIG.8A;

FIG. 9A is a top plan view of a laterally injected active distributedfeedback surface emitting laser having only one contact on the emittingsurface;

FIG. 9B is a cross-sectional view of the laterally injected activedistributed feedback surface emitting laser of FIG. 9A;

FIG. 10A is a top plan view of a laterally injected surface emittinglaser having the anode and cathode on the emitting surface;

FIG. 10B is a cross-sectional view of the laterally injected surfaceemitting laser of FIG. 10A;

FIG. 11A is a top plan view of an array of individually addressablesurface emitting diode lasers made according to the principles of thisinvention; and

FIG. 11B is a cross-sectional view of the surface emitting laser arrayof FIG. 11A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Silicon as a dopant impurity in arsenic-rich GaAs or AlGaAs prefers tooccupy a gallium site and therefore acts as a donor. Silicon is believedto diffuse by forming a mobile complex with a gallium vacancy.Accordingly impurity-induced layer disordering (IILD) of multiple layersof GaAs and AlGaAs by diffusion of silicon under arsenic-rich conditionsis known to produce only n-type wide bandgap material. On the otherhand, silicon as a dopant impurity in gallium-rich conditions prefers tooccupy the arsenic site and consequently acts as an acceptor. Becausesilicon diffuses under gallium-rich conditions by forming a complex witha gallium interstitial, it is possible to use silicon, in conjunctionwith gallium-rich annealing conditions or in a gallium-rich sourcelayer, to obtain p-type impurity-induced layer disordering of multiplelayers of GaAs and AlGaAs.

The ability to make p-type and n-type IILD regions with silicon isespecially beneficial due to the abrupt transition between thedisordered and non-disordered regions produced by the silicon diffusionfront. According to the present invention, the abruptness of thistransition enables the formation of novel semiconductor structures fromselected regions of n-type and p-type wide bandgap material produced byimpurity induced layer disordering within a multiple layer semiconductorstructure. Furthermore, according to the present invention, such devicestructures are beneficially made by simultaneously forming the n-typeand p-type IILD regions. Simultaneous formation of the n-type and p-typeIILD regions is a significant advantage since it eliminates a secondannealing which causes changes in the depth and shape of the disorderedregion produced by a first annealing. Simultaneous formation of then-type and p-type IILD regions is achieved by controlling the dopantimpurity in the silicon layer and/or by controlling the ambientenvironment during annealing, as described in U.S. Pat. No. 5,376,583,issued Dec. 24, 1994.

Simultaneous formation of n-type and p-type IILD regions allows severaltypes of novel devices to be made. One such class of devices ismonolithically integrated combinations of separate optoelectronicdevices.

For example, FIG. 1 shows an integrated device 100 comprising an N-P-Nheterojunction bipolar transistor monolithically integrated with alaterally injected edge emitting diode laser. The integratedtransistor/laser 100 comprises a semi-insulating substrate 110 of GaAs.A cladding layer 114 of p-Ga_(1-x) Al_(x) As is epitaxially deposited onthe substrate 110. An active p-type multilayer 116, which serves as theactive waveguide 121 in the laser section and as the base channel 123 inthe transistor section, is formed over the cladding layer 114. Acladding layer 120 of p-Ga_(1-x) Al_(x) As is formed over the multilayer116. The p-type multilayer 116 comprises a relatively thin conventionaldouble heterostructure active layer of p-GaAs or p-Ga_(1-y) Al_(y) As,or a single quantum well of p-GaAs or p-Ga_(1-y) Al_(y) As, or a singlequantum well of either p-GaAs or p-Ga_(1-y) Al_(y) As sandwiched betweencarrier confinement layers of p-Ga_(1-z) Al_(z) As where x>z>y, or amultiple quantum well structure of alternating well layers of p-GaAs orp-Ga_(1-y) Al_(y) As and corresponding barrier layers of either AlAs orp-Ga_(1-y') Al_(y') As sandwiched between carrier confinement layers ofGa_(1-z) Al_(z) As, where x>z≧y'>y. All of these layers may be depositedwith the well known techniques of metal organic vapor deposition ormolecular beam epitaxy.

Within the epitaxially deposited layers, an N-P-N transistor as taughtin U.S. Pat. No. 4,987,468 to Thornton and incorporated herein byreference, and separated edge emitting laser are formed to make themonolithic laser/transistor 100. The transistor of this structurecomprises an n-type disordered region 130 serving as the transistoremitter, n-type disordered region 132 as the transistor collector, andbase channel 123 formed in the p-type multilayer 116 between disorderedregions 130 and 132. The laser of this structure is formed betweenp-type disordered region 140 and n-type disordered region 132. Thus,region 132 is simultaneously the cathode of the laser and the collectorof the transistor.

When forming the first laser region and the first and second transistorregions, one or more of these regions should have an energy bandgapwhich is larger than at least the smallest energy bandgap of thematerials forming the active multilayer stratum. That is, the bandgap ofthe lowest bandgap material of the active multilayer stratum must besmaller than the bandgap of one or more of the first laser region andthe first and second transistor regions. This is true in all of thefollowing embodiments of the semiconductor laser, whether alone or whenintegrated with the semiconductor transistor, whether the laser is asurface emitting or an edge-emitting laser, and whether the region isone of the laser region and the first and second transistor regions, forthe integrated transistor/laser embodiments, or the laser anode andcathode regions, for the semiconductor laser embodiments.

The electrical connections are made to the integrated structure 100through a first metal contact layer 124, which is connected to the laseranode, a second metal contact layer 122, which is connected to thetransistor emitter, and a third metal contact layer 128, which remotelyaccesses the base channel 123. Electrical isolation between the basecontact 128 and the transistor emitter 130 is provided by the protonbombarded region 129. The proton bombarded region 126 isolates thedevice 100 from the remainder of the chip. An important feature of thedisordered region 132 is that it extends substantially through all theepitaxially deposited layers and into the semi-insulating substrate 110in order to electrically isolate the transistor from the laser.

After the layers 114-120 are formed, a shallow groove 134 is etched inthe second cladding layer 120 where the disordered region 132 will beformed. An arsenic-rich silicon layer is then deposited over the secondcladding layer 120 in the area where the n-type diffused/disorderedregions 130 and 132 will be formed. Similarly, a gallium-rich siliconlayer is deposited over the second cladding layer 120 in the area wherethe p-type diffused/disorder region 140 will be formed. Then, thearsenic-rich silicon layer and the gallium-rich silicon layer are cappedwith a silicon nitride cap layer. After the cap layer has been applied,the capped heterostructure is annealed at a high temperature.

By annealing the capped heterostructure device 100, silicon atoms in thearsenic-rich silicon layer and gallium-rich silicon layer diffuse intoheterostructure multilayers 114-120 to form the silicon impurity induceddisordered regions 130, 132 and 140. Because of the gallium-rich layer,the silicon diffuses into the heterostructure multilayers 114-120 inwhat is effectively a gallium-rich environment and the layer intermixingconsequently produced by this diffusion forms the p-type layerdisordered region 140. Because of the arsenic-rich layer, the silicondiffuses in what is effectively an arsenic-rich environment and thelayer intermixing consequently produced by this diffusion forms then-type layer disordered regions 130 and 132. The silicon diffusion isstopped after the disordered region 132 reaches the substrate 110 butbefore the disordered regions 130 and 140 reach the substrate 110.Because of the groove 134, the disordered region 132 extends deeper intothe multilayer structure than regions 130 and 140. Thus, the disorderedregion 132 isolates the base contact 128 from the active waveguide 121.Alternately, this isolation can be achieved without the groove 134 bydiffusing the silicon above region 132 for longer than the silicon aboveregions 130 and 140. This is accomplished by first depositing silicononly above region 132 and then annealing for a short period in order todrive the silicon part way into the multilayers in this region. Afterthis prediffusion, the silicon is deposited above regions 130 and 140and the annealing is continued to completion.

In an alternate method for forming integrated device 100, thearsenic-rich silicon layer, placed where disordered regions 130 and 132will be formed, is replaced with a undoped silicon layer. Accordingly,the final silicon nitride cap layer is formed only over the gallium-richsilicon layer, leaving the undoped silicon layer exposed. Then, theentire heterostructure is annealed at a high temperature in anarsenic-rich environment. Alternately, if the gallium-rich siliconlayer, rather than the arsenic-rich silicon layer, is replaced withundoped silicon, the heterostructure layers are annealed in agallium-rich environment.

By annealing the heterostructure layers in a gallium- or arsenic-richenvironment with the undoped silicon layer exposed, the exposed silicondiffuses into the heterostructure layers to form either the n-typeregions 130 and 132 or the p-type region 140, while diffusion of thecapped silicon will form the other of the n-type regions 130 and 132 orthe p-type region 140.

Alternately, an integrated transistor/laser can be formed by combiningan P-N-P transistor and a laterally injected edge emitting laser. Thegeometry of the integrated structure is the same as illustrated in FIG.1 with all the epitaxially layers doped n-type instead of p-type, thedisordered regions 130 and 132 made with p-type diffusions and thedisordered region 140 made with an n-type diffusion, according to themethods of this invention. The IILD region 130 remains the emitter ofthe transistor and the IILD region 132 remains the collector. However,the IILD region 140 becomes the cathode for the laser. The contact layer128 continues to provide remote access to the base channel 123.

A second embodiment of a heterojunction bipolar transistor integratedwith a laterally injected edge emitting diode laser is shown in FIG. 2.The integrated transistor/laser 200 comprises a substrate 210 of n-typeGaAs, upon which is grown a blocking layer 212 of undoped GaAs orAlGaAs. Before growing additional layers, portions of the blocking layer212 are removed in order to expose the underlying substrate 210. Acladding layer 214 of n-Ga_(1-x) Al_(x) As is then epitaxially grown onthe exposed portion of the substrate 210 and the remaining portion ofthe blocking layer 212. An active n-type multilayer 216, serving as theactive waveguide 221 in the laser section and as the base channel 223 inthe transistor section, is formed over the cladding layer 214. A secondcladding layer 220 of n-Ga_(1-x) Al_(x) As is formed over the multilayer216. The n-type multilayer 216 comprises a relatively thin conventionaldouble heterostructure active layer of p-GaAs or p-Ga_(1-y) Al_(y) As,or a single quantum well of p-GaAs or p-Ga_(1-y) Al_(y) As, or a singlequantum well of either p-GaAs or p-Ga_(1-y) Al_(y) As sandwiched betweencarrier confinement layers of p-Ga_(1-z) Al_(z) As where x>z>y, or amultiple quantum well structure of alternating well layers of p-GaAs orp-Ga_(1-y) Al_(y) As and corresponding barrier layers of either AlAs orp-Ga_(1-y') Al_(y') As sandwiched between carrier confinement layers ofGa_(1-z) Al_(z) As, where x>z≧y'>y. All of these layers may be depositedwith the well known techniques of metal organic vapor deposition ormolecular beam epitaxy.

Within the epitaxially deposited layers, a P-N-P transistor and aseparated edge emitting laser are formed and combined to make themonolithic laser/transistor 200. The transistor of this structurecomprises a p-type disordered region 230 serving as the transistoremitter, a p-type disordered region 232 serving as the transistorcollector, and a base channel 223 formed in the n-type multilayer 216between disordered regions 230 and 232. The laser of this structure isformed between the n-type disordered region 240 and the p-typedisordered region 232. Thus, the IILD region 232 is simultaneously theanode of the laser and the collector of the transistor. An importantfeature of the disordered region 232 is that it extends substantiallythrough all the epitaxially deposited layers and into the blocking layer212. This feature allows the n-type substrate 210 to be used to accessthe transistor base channel 223.

The electrical connections are made to the integrated structure 200through the first metal contact layer 224, which is connected to thelaser cathode, the second metal contact layer 222, which is connected tothe transistor emitter, and the third metal contact layer 228, which isconnected to the base channel 223 through the substrate 210. The protonbombarded regions 226 isolate the integrated transistor/laser 200 fromthe rest of the chip.

The integrated transistor/laser 200 is made by simultaneously formingthe n-type and p-type disordered regions by annealing the multiplelayers 212-220 and the substrate with an arsenic-rich silicon layerdeposited over the second cladding layer 220 in the area where then-type disordered region 240 will be formed and a gallium-rich siliconlayer deposited over the second cladding layer 220 in the area wherep-type disordered regions 230 and 232 will be formed, as describedabove.

An important feature of the disordered region 232 is that it extendssubstantially through all the epitaxially deposited layers and into theundoped blocking layer 212 in order to electrically isolate thetransistor from the laser. Thus the annealing process is stopped whenregions 232 and 240 penetrate the blocking layer 212 but before the IILDregion 230 reaches the substrate 210. Alternately, the deeper diffusionin region 232 can be aided by etching a groove in the second claddinglayer 220 where region 232 will be formed before depositing the siliconlayer (as shown in FIG. 1), or by diffusing the silicon above region 232for longer than the silicon above regions 230 and 240. The latterapproach is accomplished by first depositing silicon only above region232 and then annealing for a short time in order to drive the siliconpart way into the multilayers in this region. After this prediffusion,silicon is deposited above regions 230 and 240 and the annealing iscontinued to completion.

Alternately, the integrated transistor/laser 200 is made by replacingthe arsenic-rich silicon, where disordered region 240 will be formed,with an undoped silicon layer and annealing the multiple layers andsubstrate at a high temperature in an arsenic-rich environment asdescribed above. Alternately, if the gallium-rich silicon layer, ratherthan the arsenic-rich silicon layer, is replaced with undoped silicon,the multiple layers and substrate are annealed at a high temperature ina gallium-rich environment as described above.

Alternately, an integrated transistor/laser can be formed by combiningan N-P-N transistor and a laterally injected laser. The geometry of theintegrated structure is the same as illustrated in FIG. 2, except thatthe substrate and all the epitaxially layers are doped p-type instead ofn-type, the disordered regions 230 and 232 are made with n-typediffusions and the disordered region 240 is made with a p-typediffusion, according to the methods of this invention. The IILD region230 remains the emitter of the transistor and region 232 remains thecollector. However region 240 becomes the anode for the laser. Contact228 continues to provide access to the base channel 223 through thep-type substrate 210.

FIGS. 3A and 3B show an N-P-N heterojunction bipolar transistormonolithically integrated with a laterally injected surface emittinglaser, made according to the principles of this invention. Thisintegrated device is similar in some respects to the integrated deviceof FIG. 1, with a surface emitting laser used in place of the edgeemitting laser of FIG. 1. The integrated device 300 comprises thesemi-insulating substrate 110 of GaAs, upon which is epitaxiallydeposited a multilayer reflector 312, a spacer layer 314 of p-dopedGa_(1-y) Al_(y) As, a p-doped active multilayer 316, and a second spacerlayer 320 of undoped Ga_(1-y) Al_(y) As. The active multilayer 316 cancomprise a thin undoped layer of either GaAs or Ga_(1-w) Al_(w) As, oran undoped quantum well layer of either GaAs or Ga_(1-w) Al_(w) As, or amultiple quantum well structure of undoped quantum well layers of eitherGaAs or Ga_(1-w) Al_(w) As alternating with corresponding undopedbarrier layers of either AlAs of Ga_(1-v) Al_(v) As where v≧y>w. Themultilayer reflector 312 comprises an alternating stack of undopedGa_(1-z) Al_(z) As and Ga_(1-z') Al_(z') As, where z≠z', which isdesigned to provide high optical reflectivity at the lasing wavelength,as known to those skilled in the art.

Within the epitaxially deposited layers, an N-P-N transistor andseparated laser are formed to make the monolithic laser/transistor 300.The transistor of this structure comprises an n-type disordered region330 serving as the transistor emitter, an n-type disordered region 332serving as the transistor collector, and a base channel 323 which isformed in the p-type multilayer 316 between the disordered regions 330and 332. The surface emitting laser of this structure is formed betweenthe p-type disordered region 340 and the n-type disordered region 332.Thus, the IILD region 332 is simultaneously the cathode of the laser andthe collector of the transistor, while the IILD region 340 is the anodeof the laser.

An important feature of the disordered region 332 is that it extendssubstantially through all the epitaxially deposited layers and into themultilayer reflector 312 to form the cylindrical optical waveguide forthe surface emitting laser. This feature also isolates the transistorbase 328 from the laser.

Proton bombardment in regions 127 provides electrical isolation betweenthe cathode/collector 332 and the anode 340 within the heterostructurelayers. Alternately, the p-type and n-type diffusions can overlap in theproton bombardment regions 127 to form a p-n junction in the widebandgap material. The optical mirrors of the laser cavity are formed bythe multilayer reflector 312 and the dielectric or semiconductormultilayer stack 362, which is formed on the surface of the secondspacer layer 320.

The electrical contacts are made to the integrated structure 300 throughthe first metal contact layer 324, which is connected to the laser anode340, the second metal contact layer 322, which is connected to thetransistor emitter 330, and the third metal contact layer 328, which isconnected to the base 323 through the spacer layer 320. Protonbombardment in region 129 isolates the transistor base from thetransistor emitter within the heterostructure layers. Proton bombardedregions 126 isolate the integrated transistor/laser 300 from the rest ofthe chip.

After the layers 312-320 are formed, steps are taken to ensure that thedisordered region 332 penetrates into the multilayer reflector 312during the subsequent annealing. This penetration may be accomplished byforming a shallow groove 134 where cathode/collector 332 will be formed,as shown in FIG. 3B, or by removing a portion of the second spacer layer320 only where cathode/collector 332 and anode 340 will be formed. Theintegrated transistor/laser 300 is then made by simultaneously formingthe n-type and p-type disordered regions 330, 332 and 340 by annealingthe multiple layers 312-320 and the substrate 110 with an arsenic-richsilicon layer deposited over the second spacer layer 320 in the areawhere the n-type emitter 330 and the n-type cathode/collector 332 willbe formed and a gallium-rich silicon layer deposited over the layer 320in the area where the p-type anode 340 will be formed, as describedabove.

Alternately, the integrated transistor/laser 300 is made by replacingthe arsenic-rich silicon, where n-type emitter 330 and the n-typecathode/collector 332 will be formed, with an undoped silicon layer andannealing the multiple layers and substrate at a high temperature in anarsenic-rich environment as described above. Alternately, if thegallium-rich silicon layer, rather than the arsenic-rich silicon layer,is replaced with undoped silicon, the multiple layers and substrate areannealed at a high temperature in a gallium-rich environment, asdescribed above.

Alternately, an integrated transistor/laser can be formed by combiningan P-N-P transistor and a laterally injected surface emitting laser. Thegeometry of the integrated structure is the same as illustrated in FIGS.3A and 3B with all the epitaxially layers doped n-type instead ofp-type, the disordered regions 330 and 332 made with p-type diffusionsand the disordered region 340 made with an n-type diffusion, accordingto the method of this invention. The region 330 remains the emitter ofthe transistor and the region 332 remains the collector. However, theregion 340 becomes the cathode for the the laser. The contact 328continues to provide remote access to the base channel 323.

A second embodiment of a heterojunction bipolar transistor integratedwith a laterally injected surface emitting diode laser is shown in FIGS.4A and 4B. The integrated transistor/laser 400 comprises the substrate210 of n-type GaAs, upon which is grown a multilayer reflector 412.Before growing additional layers, portions of the multilayer 412 areremoved in order to expose the underlying substrate. A spacer layer 414of n-Ga_(1-x) Al_(x) As is then epitaxially grown on the exposed portionof substrate 210 and the remaining portion of the multilayer 412. Anactive n-type multilayer 416 is formed over the spacer layer 414. Asecond spacer layer 420 of undoped Ga_(1-x) Al_(x) As is formed over themultilayer 416. The n-type multilayer 416 comprises a relatively thinconventional double heterostructure active layer of n-GaAs or n-Ga_(1-y)Al_(y) As, or a single quantum well of n-GaAs or n-Ga_(1-y) Al_(y) As,or a single quantum well of either n-GaAs or n-Ga_(1-y) Al_(y) Assandwiched between carrier confinement layers of n-Ga_(1-z) Al_(z) Aswhere x>z>y, or a multiple quantum well structure of alternating welllayers of n-GaAs or n-Ga_(1-y) Al_(y) As and corresponding barrierlayers of either AlAs or n-Ga_(1-y') Al_(y') As sandwiched betweencarrier confinement layers of Ga_(1-z) Al_(z) As, where x>z≧y'>y. All ofthese layers may be deposited with the well known techniques ofmetalorganic vapor deposition or molecular beam epitaxy.

Within the epitaxially deposited layers, an P-N-P transistor andseparated surface emitting laser are formed to make the monolithiclaser/transistor 400. The transistor of this structure comprises ap-type disordered region 430 serving as the transistor emitter, a p-typedisordered region 432 serving as the transistor collector, and a basechannel 423 formed in the n-type multilayer 416 between the disorderedregions 430 and 432. The surface emitting laser of this structure isformed between the n-type disordered region 440 and the p-typedisordered region 432. Thus, the n-type region 440 is the laser cathodeand the p-type region 432 is simultaneously the anode of the laser andthe collector of the transistor. An important feature of theanode/collector 432 is that it extends substantially through all theepitaxially deposited layers and into the multilayer reflector 412 toform the cylindrical optical waveguide for the surface emitting laser.

Proton bombardment in regions 127 provides electrical isolation betweenthe anode/collector 432 and the cathode 440 of the laser within theheterostructure layers. Alternately, the p-type and the n-typediffusions can overlap in regions 127 to form a p-n junction in widebandgap material. The optical mirrors of the laser cavity are formed bythe multilayer reflector 412 and the dielectric or semiconductormultilayer stack 462, which is formed on the surface of the spacer layer420.

The electrical contacts are made to the integrated structure 400 throughthe first metal contact layer 124, which is connected to the lasercathode 440, the second metal contact layer 122, which is connected tothe transistor emitter 430, and the third metal contact layer 128, whichis connected to the base 423 through the substrate 210. The protonbombarded regions 126 isolate the integrated transistor/laser 400 fromthe rest of the chip

The integrated transistor/laser 400 is made by simultaneously formingthe n-type and p-type disordered regions by annealing the multiplelayers 412-420 and the substrate with an arsenic-rich silicon layerdeposited over the second spacer layer 420 in the area where the n-typecathode 440 will be formed and a gallium-rich silicon layer depositedover the second spacer layer 420 in the area where the p-type emitter430 and the p-type anode/collector 432 will be formed, as describedabove. Alternately, the integrated transistor/laser 400 is made byreplacing the arsenic-rich silicon, at a point above where cathode 440is to be formed, with an undoped silicon layer, then annealing themultiple layers and substrate at a high temperature in an arsenic-richenvironment as described above. Alternately, if the gallium-rich siliconlayer, rather than the arsenic-rich silicon layer, is replaced withundoped silicon, the multiple layers and substrate are annealed at ahigh temperature in a gallium-rich environment, as described above.

Alternately, an integrated transistor/laser can be formed by combiningan N-P-N transistor and a laterally injected surface emitting laser. Thegeometry of the integrated structure is the same as illustrated in FIGS.4A and 4B, except that the substrate and all the epitaxially layers aredoped p-type, instead of n-type, the disordered regions 430 and 432 madewith n-type diffusions and disordered region 440 are made with an p-typediffusion, according to the method of this invention. The region 430remains the emitter of the transistor and the region 432 remains thecollector. However, the region 440 becomes the anode for the laser. Thecontact 128 continues to provide access to the base channel 423 throughthe p-type substrate 210.

A third class of devices enabled by simultaneous formation of the n-typeand p-type IILD regions according to this invention contain buriedlayers which are to be individually contacted with a wide bandgapemitter or collector. The individual layers may require p-type, n-type,or p-type and n-type contacting. Structures of this type can be used,for example, to make carrier channeling structures, "n-i-p-i" or hetero"n-i-p-i" devices, or p-n junction surface emitting lasers.

FIGS. 5A and 5B show a surface emitting laser 500 made according to theprinciples of this invention. The surface emitting laser 500 comprisesthe semi-insulating substrate 110 of GaAs, upon which is epitaxiallydeposited a wide bandgap buffer layer 518 of undoped Ga_(1-x) Al_(x) As,a multilayer reflector 512, a spacer layer 514 of undoped Ga_(1-y)Al_(y) As, where x≧y, an undoped active multilayer 516, a second spacerlayer 520 of undoped Ga_(1-y) Al_(y) As, and a dielectric orsemiconductor multilayer stack 562 deposited on the surface of thesecond spacer layer 520. The multilayer 516 comprises either a thinundoped layer of either GaAs or Ga_(1-w) Al_(w) As, an undoped quantumwell layer of either GaAs or Ga_(1-w) Al_(w) As, or a multiple quantumwell structure of undoped quantum well layers of either GaAs or Ga_(1-w)Al_(w) As alternating with corresponding undoped barrier layers ofeither AlAs or Ga_(1-v) Al_(v) As, where v≧y>w. The multilayer reflector512 comprises an alternating stack of undoped Ga_(1-z) Al_(z) As andGa_(1-z') Al_(z') As, where z≠z', which is designed to provide highoptical reflectivity at the lasing wavelength, as known to those skilledin the art. Similarly, multilayer 562 comprises an alternating stack ofsemiconductor or dielectric layers, which is designed to provide highoptical reflectivity at the lasing wavelength.

The surface emitting laser 500 is defined within the epitaxiallydeposited layers by semi-annular cathode 530 and semi-annular anode 540.The cathode 530 comprises an n-type wide bandgap material formed byimpurity induced layer disordering of the as-grown multiple layers,andserves as the electron source for the undoped active layer 516. Theanode 540 comprises a p-type wide bandgap material formed by impurityinduced layer disordering of the as-grown multiple layers, and serves asthe hole source for the undoped active layer 516. The cathode 530 andthe anode 540 beneficially extend through the reflector 512 and into thewide bandgap layer 518 to form the cylindrical optical waveguide for thesurface emitting laser 500. Proton bombardment in regions 127 provideselectrical isolation between the cathode 530 and the anode 540 withinthe heterostructure layers. Alternately the p-type and n-type diffusionscan overlap in regions 127 to form a p-n junction in the wide bandgapmaterial. The optical mirrors of the laser cavity are formed by themultilayer reflector 512 and the dielectric or semiconductor multilayerstack 562.

The electrical connections are made to laser 500 through the cathodemetal contact layer 522, which is connected to the cathode 530 and theanode metal contact layer 524, which is connected to the anode 540.Proton bombardment in regions 126 isolates the laser 500 from the restof the chip. Finally, the multiple layer dielectric reflector 562 isformed in the center of the annular metal layers forming the cathodecontact 522 and the anode contact 524.

In the surface emitting laser 500, holes are injected from the anode540, while electrons are injected from the cathode 530. In the surfaceemitting laser 500, both electrons and holes are injected into theactive layer without passing through either the distributed Braggreflector 512 or the dielectric stack 562 used to form the laser cavity.Thus, the surface emitting laser 500 inherently has a low seriesresistance compared to conventional surface emitting lasers, in whichcarriers must pass through many high bandgap layers.

The surface emitting laser 500 is made by simultaneously forming then-type and p-type disordered regions by annealing the multiple layers512-520 and substrate 110 with an arsenic-rich silicon layer depositedover the second spacer layer 520 in the area where the cathode 530 willbe formed and a gallium-rich silicon layer deposited over the secondspacer layer 520 in the area where anode 540 will be formed, asdescribed above. Alternately, the surface emitting laser 500 is made byreplacing the arsenic-rich silicon, above the region where cathode 530will be formed, with an undoped silicon layer and annealing the multiplelayers and substrate at a high temperature in an arsenic-richenvironment as described above. Alternately, if the gallium-rich siliconlayer rather than the arsenic-rich silicon layer is replaced withundoped silicon, the multiple layers and substrate are annealed at ahigh temperature in a gallium-rich environment as described above.

FIGS. 6A and 6B show a carrier channeling device 600 made according tothe principles of this invention. The channeling structure 600 comprisesthe semi-insulating substrate 110 of GaAs, upon which is epitaxiallydeposited an undoped wide bandgap buffer layer 618 of undoped Ga_(1-x)Al_(x) As, an active multilayer 616, and a wide bandgap cladding layer620 of undoped Ga_(1-x) Al_(x) As. The multilayer 616 comprises thinlayers 616a, c, e, etc of p-doped GaAs or Ga_(1-y) Al_(y) As alternatingwith thin layers 616b, d, f, etc of n-doped GaAs or Ga_(1-z) Al_(z) As,where x≧y≧z.

The channeling device 600 is defined within the epitaxially depositedlayers by the cathode 630 and the anode 640. The cathode 630 comprisesan n-type disordered region serving as the wide bandgap contact for tilen-doped layers 616a, c, e, etc. The interface 627, as viewed from thetop between the cathode 630 and each n-doped layer, can be shaped asdesired, e.g. it can be circular, elliptical, linear, etc. The anode 640comprises a p-type disordered region serving as the wide bandgap contactfor the p-doped layers 16b, d, f, etc. The interface 625, as viewed fromthe top between the anode 640 and each p-doped layer, can be shaped asdesired, e.g. it can be circular, elliptical, linear, etc. Theelectrical connections are made to the carrier channeling device 600through the cathode metal layer contact 622, which is connected to thecathode 630 and the anode metal layer contact 624, which is connected tothe anode 640. A surface region 642 is left open between the contactsfor optical access. Proton bombardment in regions 126 isolates thedevice 600 from the rest of the chip.

The carrier channeling device 600 is made by simultaneously forming then-type and p-type disordered regions as described above. The channelingdevice 600 can be used, for example, as a channeling photodiode asdisclosed by F. Capasso, et al. in Appl. Phys. Letters vol 41(10), pp944-946 Nov. 15, 1982, by exposing the surface 642 with the light to bedetected. However, Capasso teaches that the p- and n-doped contactregions are defined either by ion implantation or etching and epitaxialregrowth techniques. Ion implantation can dope the layers appropriatelybut does not increase their bandgap. Etching and regrowth can produce anappropriately doped wide bandgap contact but is a low yield, expensive,and unreliable process. The simultaneous formation of n-type and p-typewide bandgap contacts according to the principles of this invention is asignificant improvement in design which allows low-cost, high yield,reliable fabrication.

FIG. 7 shows an expanded view of the active layer 716 for a "nipi"device made according to the principles of this invention. Themultilayer active layer 716 comprises thin layers 652a, b, c, etc. ofundoped GaAs or Ga_(1-u) Al_(u) As, sandwiched between alternating thinlayers 654a, b, c, etc of n-doped GaAs or Ga_(1-v) Al_(v) As and thinlayers 656a, b, c, etc of p-doped GaAs or Ga_(1-w) Al_(w) As, where v≧uand w≧u. The geometrical structure for the "nipi" device is the same asfor the carrier channeling device shown in FIGS. 6A and 6B, with theactive multilayer 716 shown in FIG. 7 replacing the standard activemultilayer 616 of the carrier channeling device 600.

Such a "nipi" device can be used to make a wide range of devices withadjustable conductivity, adjustable absorption, or tunable luminescence,as disclosed by G. H. Dohler, and K. Ploog, in Synthetic ModulatedStructures, edited by L. L. Chang and B.C. Glessin, Academic Press,1985, New York, pp 163-214. However Dohler teaches that the p- andn-doped contact regions are defined by alloying p-type and n-typeelements such as Sn and Zn into the multiple layers. Such alloying canappropriately dope the layers but can not increase the bandgap of thedoped layers. Etching followed by regrowth could produce appropriatelydoped wide bandgap contacts but is a low yield, expensive, andunreliable process. The simultaneous formation of n-type and p-type widebandgap contacts according to the principles of this invention is asignificant improvement in design which enables low-cost, high yield,reliable fabrication of "nipi" devices. The wide bandgap contacts areespecially advantageous because they suppress carrier leakage between acontact and a layer of opposite polarity while enhancing carrierinjection between a contact and a layer of the same polarity.

A fourth class of devices enabled by simultaneous formation of n-typeand p-type IILD regions according to the principles of this inventionconsist of novel interdigitated structures, as shown in FIGS. 8A and 8B.Structures of this type can be used, for example, to make fast opticaldetectors or edge-emitting distributed feedback lasers. One embodimentof an interdigitated structure made according to this invention is shownin FIG. 8A and 8B. As shown in FIG. 8B, the interdigitated structure 800comprises the semi-insulating substrate 110 of GaAs, upon which isepitaxially deposited a wide bandgap layer 812 of undoped Ga_(1-x)Al_(x) As, an undoped active multilayer 816, and a second wide bandgaplayer 820 of undoped Ga_(1-y) Al_(y) As. The layers contained in theactive multilayer 816 will depend on the intended function of theinterdigitated structure. For example, if the interdigitated structureis a pin photodiode, multilayer 816 can comprise a single undoped layerof GaAs or a multiple quantum well structure of undoped quantum welllayers of GaAs alternating with corresponding undoped barrier layers ofeither AlAs or Ga_(1-v) Al_(v) As. The incident optical wave is absorbedin the GaAs layers of either multilayer. Alternately, if theinterdigitated structure is a distributed feedback laser, the multilayer816 can comprise an active layer configuration suitable for laseroperation, e.g. an undoped quantum well layer of either GaAs or Ga_(1-w)Al_(w) As, or a multiple quantum well structure of undoped quantum welllayers of either GaAs or Ga_(1-w) Al_(w) As alternating withcorresponding undoped barrier layers of either AlAs of Ga_(1-v) Al_(v)As where v≧y>w.

The interdigitated structure is defined within the epitaxially depositedlayers by the n-type diffused/disordered regions 830, which alternatewith the p-type diffused/disordered regions 840. Since the disorderedregions of opposite polarity do not touch or overlap, regions of lowbandgap 850 are formed in active layer 816 between the disorderedregions 830 and 840. A single electrical contact 822 is made to all ofthe n-type diffused/disordered regions 830 and a single electricalcontact 824 is made to all of the p-type diffused/disordered regions840. The contacts 822 and 824 can extend partly or entirely over each ofthe n-type and p-type regions 830 and 840, respectively. Likewise, thelaterally extending regions 830 and 840 may overlap only in part or oversubstantially their entire length, as shown in FIG. 8A.

The interdigitated structure 800 is made by simultaneously forming then-type and p-type disordered regions 830 and 840, as described above.

The interdigitated structure 800 with an appropriate active layer 816operates as a p-i-n optical detector by applying a positive voltage onthe contact 822 relative to the contact 824. This bias conditioneffectively reverse biases the undoped regions 850, thereby establishingan electric field within the regions 850 which sweeps electrons to then-doped regions 830 and holes to the p-doped regions 840. The light tobe detected is introduced into the detector 800 either in a directionnormal to the active multilayer 816 between the interdigitated fingersof the contacts 822 and 824 or in the waveguide formed between the widebandgap layers 812 and 820. The absorption of photons in the undopedregions 850 produces electron/hole pairs, which are swept out of theregions 850 and into the regions 830 and 840 by the electric fieldestablished by the bias voltage on the contacts 822 and 824.

Alternately, a similar structure can be used as a gain-coupleddistributed feedback laser by applying a positive voltage on the contact824 relative to the contact 822. This voltage polarity forward biasesthe anode regions 840 and the cathode regions 830, thereby injectingcarriers into the low bandgap regions 850. The injected carriers in theregions 850 then provide the optical gain required for lasing operation.Distributed optical feedback is obtained by choosing thecenter-to-center spacing of the regions 850 and the center-to-centerspacing between any region 830 and its adjacent regions 840 to be equalto an integer number of half wavelengths of the desired lasingwavelength in the semiconductor medium. At these spacings, reflectionsof the optical waves from the gain in the regions 850 and the changes inthe refractive index at the interfaces between the regions 830 and 840establish the well-known Bragg condition, thus producing distributedoptical feedback in the active layer 816. For example, thecenter-to-center spacing of the regions would be about 0.11 μm, or 0.22μm, or 0.33 μm, etc. for an emission wavelength of 780 nm.

FIGS. 9A and 9B show a first embodiment of a laterally injected activedistributed feedback surface emitting laser 900 made according to theprinciples of this invention. The laser 900 comprises the conductivesubstrate 210 of n-doped GaAs, a wide bandgap buffer layer 920 ofn-Ga_(1-x) Al_(x) As, an active undoped multilayer 916, and a widebandgap window layer 912 of undoped Ga_(1-y) Al_(y) As, where y≧x. Theundoped multilayer 916 comprises a periodic sequence of active quantumwell layers of undoped GaAs or undoped Ga_(1-z) Al_(z) As, alternatingwith barrier layers of undoped Ga_(1-z') Al_(z') As, wherein z'>z.Typically, the total number of periods in the alternating layer sequenceis greater than 25 (i.e. greater than 50 layers).

The period of the alternating layers is chosen to be approximately 1/2of the desired lasing wavelength in the semiconductor material. Forexample, for an emission wavelength of 780 nm, the center to centerspacing of the quantum wells is about 1100 nm. The periodicity of thelayer structure is a critical parameter for effective operation of thesurface emitting laser at a desired wavelength. The thickness andcomposition of each quantum well is chosen to maximize the gain at theemission wavelength. For 780 nm, each quantum well may comprise Ga₀.88Al₀.12 As of 150 nm thickness.

Preferably, each of the quantum well layers of the multilayer 916 (aswell as the multilayer 1016) is formed from one of the followingmaterials: gallium arsenide, gallium aluminum arsenide, gallium indiumphosphide and aluminum gallium indium phosphate. In the multilayer 916(and the multilayer 1016) these materials are undoped. Likewise, each ofthe barrier layers of the multilayer 916 (as well as the multilayer1016) as formed from one of the following materials: gallium aluminumarsenide; aluminum arsenide, aluminum indium phosphide and aluminumgallium indium phosphide. In the multilayer 916 (as well as themultilayer 1016), these materials are undoped.

The composition of each barrier layer is chosen to be transparent at thelasing wavelength and to provide adequate carrier confinement ofcarriers in the quantum wells. For 780 nm, each barrier layer maycomprise Ga_(1-z') Al_(z') As with z'<0.4 and have a thickness of 950nm. The value of z' is restricted to low values by the heat generated inpassing current through the undoped barrier layers. The interfacebetween the quantum well and the barrier layer may be graded to reducethe voltage. Other combinations of composition and thickness for thequantum well in conjunction with other combinations of composition andthickness for the barrier layer may be used to optimize the structurefor operation at a wavelength of 780 nm. As is known in the art, theepitaxial growth of these layers may be carried out by molecular beamepitaxy (MBE) or metalorganic chemical vapor deposition (MOCVD).

The surface emitting laser 900 is defined within the epitaxiallydeposited layers by the p-type disordered region 940. The p-typedisordered region 940 is formed in an annulus, which beneficiallyextends through the active multilayer 916 and into the wide bandgaplayer 920, to form a cylindrical optical waveguide for the surfaceemitting laser 900. The p-type disordered region 940 serves as the holesource for the active quantum wells in the multilayer 916. The annulusmay be circular, as shown in FIG. 9A, or elliptical or square or anyother desired shape.

The electrical contacts are made to the surface emitting laser 900through the anode metal contact layer 936, which is connected to thep-type disordered region 940, and the cathode metal contact layer 938,which is connected to the substrate 210. The cathode metal contact layer936 has an opening 937 centered on the undisordered portion of themultilayer 916 to allow light emission from the laser 900. A protonbombardment in the region 126 isolates the laser 900 from the otherparts of the chip. Finally, an anti-reflective coating 962 is formed inthe center of the annular portion of the anode metal contact layer 936.

The surface emitting laser 900 is made by forming the p-type disorderedregion 940 within the multiple semiconductor layers 912-920. Thedisordered region 940 is formed by annealing the multiple layers 912-920and the substrate 210 with a gallium-rich silicon layer deposited overthe layer 912 in the area where the p-type disordered region 940 will beformed, as described in U.S. Pat. No. 5,376,583, issued Dec. 24, 1994.Alternately, the surface emitting laser 900 is made by replacing thegallium-rich silicon above where the disordered region 40 will be formedwith an undoped silicon layer and annealing the multiple layers and thesubstrate at a high temperature in a gallium-rich environment, as isalso described in U.S. Patent 5,376,583, issued Dec. 24, 1994.

In the surface emitting laser 900, holes are injected into the quantumwells of the multilayer 916 from the p-type disordered region 940, whileelectrons are injected into the quantum wells from the substrate 210through the buffer layer 920 and the barrier layers in multilayer 916.Thus, the current flows from a current source (not shown in FIGS. 9A and9B), into the anode metal contact layer 936, through the disorderedregion 940, through the quantum well layers in the multilayer 916,through the barrier layers in the multilayer 916, through the bufferlayer 920, through the substrate 210 into the cathode metal contactlayer 938 and back to the current source. The recombination of electronsand holes in the quantum wells of the multilayer 916 provides theoptical gain required to produce lasing. Coupling of the forward andbackward travelling optical waves by the periodic gain and periodicrefractive index produced by the multiple alternating layers in themultilayer 916 produces the distributed optical feedback required tosustain lasing oscillation. Light is emitted from the laser 900 throughanti-reflective coating 962. The coating 962 substantially eliminatesoptical reflections from the index change at the air/semiconductorinterface, which may disturb the distributed optical feedback.

Alternately, the surface emitting laser 900 can be formed by using ann-type impurity induced layer disordering instead of the p-typedisordering process described above. The geometry of the surfaceemitting laser remains the same as illustrated in FIGS. 9A and 9B, withthe substrate 210 and the buffer layer 920 doped p-type instead ofn-type. The metal contact layer 936 is then the laser cathode and themetal contact layer 938 is the laser anode. N-type layer disordering iswell known to those skilled in the art and is taught in U.S. Pat. No.4,824,798.

FIGS. 10A and 10B show a second embodiment of a laterally injectedactive distributed feedback surface emitting laser 1000 made accordingto the principles of this invention. The laser 1000 comprises thesemi-insulating substrate 110 of GaAs, upon which is epitaxiallydeposited a wide bandgap buffer layer 1020 of n-Ga_(1-x) Al_(x) As, anactive undoped multilayer 1016, and a wide bandgap window layer 1012 ofundoped Ga_(1-y) Al_(y) As, where y≧x. The undoped multilayer 1016comprises a periodic sequence of active quantum wells of undoped GaAs orundoped Ga_(1-z) Al_(z) As alternating with barrier layers of undopedGa_(1-z') Al_(z') As, similar to that described in relation to FIGS. 9Aand 9B. However, in the present embodiment, the Al content of thebarrier layers can be much greater than in the embodiment of FIGS. 9Aand 9B. For example, z' can be greater than 0.8, thereby providingmaximum carrier confinement in the quantum wells of multilayer 1016.

The period of the alternating layers is again chosen to be approximately1/2 of the desired lasing wavelength in the semiconductor material inorder to provide distributed optical feedback and the thickness andcomposition of each quantum well is chosen to maximize the gain at theemission wavelength. As is known in the art, the epitaxial growth ofthese layers may be carried out by molecular beam epitaxy (MBE) ormetalorganic chemical vapor deposition (MOCVD).

The surface emitting laser 1000 is defined within the epitaxiallydeposited layers by the semi-annular region 1030 and the semi-annularregion 1040. The region 1030 comprises an n-type wide bandgap materialformed by impurity induced layer disordering of the as-grown multiplelayers. The n-type disordered region 1030 serves as the electron sourcefor the undoped quantum wells in the multilayer 1016. The region 1040comprises a p-type wide bandgap material formed by impurity inducedlayer disordering of the as-grown multiple layers. The p-type disorderedregion 1040 serves as the hole source for the undoped quantum wells inthe multilayer 1016. The disordered regions 1030 and 1040 beneficiallyextend through the active multilayer 1016 and into the wide bandgaplayer 1020 to form the cylindrical optical waveguide for the surfaceemitting laser 1000. A proton bombardment in regions 127 provideselectrical isolation within the heterostructure layers between thedisordered region 1030 and the disordered region 1040. Alternately, thep-type and n-type diffusions can overlap in the regions 1027 to form ap-n junction in the wide bandgap material.

The electrical connections are made to the laser 1000 through thecathode metal contact layer 1036, which is connected to the disorderedregion 1030 and the anode metal contact layer 1038, which is connectedto the disordered region 1040. The semiannular metal contact layers forthe cathode and anode contacts 1036 and 1038 form an opening around theundisordered portion of the multilayer 1016 for light emission. A protonbombardment in the regions 126 isolates the laser 1000 from other partsof the chip. Finally, the multiple layer dielectric reflector 1062 isformed in the center of the semiannular metal contact layers forming thecathode contact 1036 and the anode contact 1038.

The surface emitting laser 1000 is made by simultaneously forming then-type and p-type disordered regions within the multiple semiconductorlayers 1012-1020. The disordered regions 1030 and 1040 are formed byannealing the multiple layers 1012-1020 and the substrate 110 with anarsenic-rich silicon layer deposited over the layer 1012 in the areawhere the n-type disordered region 1030 will be formed and agallium-rich silicon layer deposited over layer 1012 in the area wherethe p-type disordered region 1040 will be formed, as described in U.S.patent application Ser. No. unassigned, Attorney Docket No. JAO 28198.Alternately, the surface emitting laser 1000 is made by replacing thearsenic-rich silicon above where the disordered region 1030 will beformed with an undoped silicon layer and annealing the multiple layersand substrate at a high temperature in an arsenic-rich environment.Alternately, if the gallium-rich silicon layer, rather than thearsenic-rich silicon layer, is replaced with undoped silicon, themultiple layers and substrate are annealed at a high temperature in agallium-rich environment.

in the surface emitting laser 1000, holes are injected into the quantumwells of the multilayer 1016 from the p-type disordered region 1040,while electrons are injected from the n-type disordered region 1030.Thus, the current flows from a current source (not shown in FIGS. 10Aand 10B), into the anode contact 1038, through the disordered region1040, through the active quantum wells in the multilayer 1016, throughthe disordered region 1030, into the cathode contact 1036 and back tothe current source. In the surface emitting laser 1000, the currentflows through the active multilayer 1016 without passing through thebarrier layers. Thus, the surface emitting laser 1000 inherently has alower series resistance than the surface emitting laser of theembodiment of FIGS. 9A and 9B, wherein the carriers must pass throughmany high bandgap barrier layers. Consequently, there is no need tograde the interface between the quantum wells and the barrier layers, asis often done by those skilled in the art. Thus, the laser 1000 is apreferred form of this embodiment of the invention.

The recombination of electrons and holes in the quantum wells of themultilayer 1016 provides the optical gain required to produce lasing.Coupling the forward and backward travelling optical waves by theperiodic gain and periodic refractive index produced by the multiplealternating layers in the multilayer 1016 produces the distributedoptical feedback required to sustain the lasing oscillation. Light isemitted from the laser 1000 through the anti-reflective coating 1062.The coating 1062 substantially eliminates optical reflections from theindex change at the air/semiconductor interface, which may influence thedistributed optical feedback.

FIGS. 11A and 11B illustrate a high density array 1100 of independentlyaddressable surface emitting lasers, made according to the principles ofthis invention. Each laser element 1142 in this array 1100 is formedidentically to the laser 1000 described in FIGS. 10A and 10B. As shown,the contacts 1136 and 1138 for each laser element 1142 are formedseparately and isolated from the contacts of the other laser elements1142. Alternately, all the anodes 1138 or all the cathodes 1136 have acommon metal contact layer if they are to be connected to a commonground. In either case, at least the cathode contact 1136 or the anodecontact 1138 for each laser element 1142 remains isolated from the othercontacts (1136 or 1138) for the other laser elements 1142, so that eachlaser element 1142 can be modulated independently from the other laserelements 1142.

Alternately, the array 1100 can comprise surface emitting laser elements1142 made identically to the laser 900 described in FIGS. 9A and 9B. Inthis case, each laser has its own addressable contact 1136 or 1138 onthe top surface. The other contact 1138 or 1136 on the substrate is thencommon to all the laser elements 1142. Finally, each laser element 1142may be made with either p-type disordering or n-type disordering.

While this invention has been described in conjunction with a number ofdifferent specific apparatus, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications and variations as fall within the spirit and broad scopeof the appended claims.

What is claimed is:
 1. A surface emitting laser, comprising:a substrate;a multilayer optical reflecting stratum formed over the substrate; afirst wide bandgap spacer layer formed over the multilayer reflectingstratum; an light emitting multilayer stratum formed over the firstspacer layer; a second wide bandgap spacer layer formed over the lightemitting stratum; an annular contact region formed over the secondspacer layer; a set of multiple layers, the multiple layers formed fromone of dielectric materials and semiconductor materials, the set ofmultiple layers formed over the second spacer layer in a center portionof the annular contact region; a first semi-annular laser region formedin the second spacer layer under a first semi-annular portion of theannular contact region and extending through the active light emittingstratum, the first spacer layer, and into the multilayer reflectingstratum; and a second semi-annular laser region formed in the secondspacer layer under a second semi-annular portion of the annular contactregion and extending through the active light emitting stratum, thefirst spacer layer, and into the multilayer reflecting stratum; whereinthe first and second laser regions are formed of oppositely dopedmaterials to function as the laser cathode and laser anode.
 2. Thesurface emitting laser of claim 1, wherein one of said laser regions isformed from material having a bandgap larger than the bandgap of alowest bandgap material present in said light emitting stratum.
 3. Thesurface emitting laser of claim 1, wherein one of the laser regions isformed by impurity induced layer disordering.
 4. The surface emittinglaser of claim 1, further comprising a wide bandgap buffer layer formedbetween the substrate and the multilayer optical reflecting stratum,wherein said first and second semiannular laser regions extend into saidbuffer layer.
 5. An array of surface emitting semiconductor laserscomprising a plurality of the surface emitting laser of claim
 1. 6. Thearray of surface emitting semiconductor lasers of claim 5, wherein eachone of the plurality of lasers has one of an independent anode contactand a common anode contact and each one of the plurality of lasers hasone of an independent cathode contact and a common cathode contact.
 7. Asurface emitting semiconductor laser, comprising:a substrate having afirst doping type; a wide bandgap buffer layer formed over the substrateand having a first doping type; an active undoped multilayer stratumformed over the wide bandgap buffer layer; a wide bandgap window layerformed over the active multilayer stratum; an annular wide bandgapregion formed in the wide bandgap window layer and extending through theactive multilayer stratum into the wide bandgap buffer layer, theannular wide bandgap region having a second doping type; a first metalcontact layer formed over at least the annular wide bandgap region; anda second metal contact layer formed over a surface of the substrateopposite from the wide bandgap buffer layer; wherein the active undopedmultilayer stratum is an alternating periodic layer structure comprisinga plurality of light emitting low bandgap quantum well layersalternating with a plurality of wide bandgap layers, the alternatingperiodic layer structure providing optical gain and optical feedback forlasing operation.
 8. The surface emitting laser of claim 7, wherein saidannular wide bandgap region is formed by impurity induced layerdisordering.
 9. The surface emitting semiconductor laser of claim 8,wherein:the substrate and the wide bandgap buffer layer are dopedn-type; the annular IILD region is doped p-type; the first metal contactlayer is an anode contact; and the second metal contact layer is acathode contact.
 10. The surface emitting semiconductor of claim 8,wherein:the substrate and the wide bandgap buffer layers are dopedp-type; the annular IILD region is doped n-type; the first metal contactlayer is a cathode contact; and the second metal contact layer is ananode contact.
 11. The surface emitting semiconductor laser of claim 7,wherein a period of the alternating layers is approximately one-half adesired lasing wavelength.
 12. The surface emitting semiconductor laserof claim 7, further comprising an anti-reflective coating formed overthe wide bandgap window layer in a center portion of the annular widebandgap region.
 13. An array of surface emitting semiconductor lasers,comprising a plurality of the surface emitting lasers of claim
 7. 14.The array of surface emitting semiconductor lasers of claim 13, whereineach one of the plurality of lasers has one of an independent anodecontact and a common anode contact and each one of the plurality oflasers has one of an independent cathode contact and a common cathodecontact.
 15. A surface emitting semiconductor laser, comprising:asemi-insulating substrate; an undoped wide bandgap buffer layer formedover the substrate; an active undoped multilayer stratum formed over thewide bandgap buffer layer; a wide bandgap window layer formed over theactive undoped multilayer stratum; an annular wide bandgap region formedin the wide bandgap window layer and extending through the activeundoped multilayer stratum into the wide bandgap buffer layer, a firstsemi-annular portion of the annular wide bandgap region having a firstdoping type and a second semi-annular portion having a second dopingtype; a first metal contact layer formed over the wide bandgap windowlayer and contacting the first semi-annular portion; and a second metalcontact layer formed over the wide bandgap window layer and contactingthe second semi-annular portion; wherein the active undoped multilayerstratum is an alternating periodic layer structure comprising aplurality of light emitting low bandgap quantum well layers, eachalternating with one of a plurality of wide bandgap layers, thealternating periodic layer structure providing optical gain and opticalfeedback for lasing operation.
 16. The surface emitting laser of claim15, wherein one of said semi annular portions of said annular widebandgap region is formed by impurity induced layer disordering.
 17. Thesurface emitting semiconductor laser of claim 15, wherein:the firstsemi-annular portion of the annular wide bandgap region is doped p-type;the second semi-annular portion is doped n-type; the first metal contactlayer is an anode contact; and the second metal contact layer is acathode contact.
 18. The surface emitting semiconductor laser of claim15, wherein a period of the alternating layers is approximately one-halfa desired lasing wavelength.
 19. The surface emitting semiconductorlaser of claim 15, further comprising an anti-reflective coating formedover the wide bandgap window layer in a center portion of the annularwide bandgap region.
 20. An array of surface emitting semiconductorlasers comprising a plurality of the surface emitting laser of claim 15.21. The array of surface emitting semiconductor lasers of claim 20,wherein each one of the plurality of lasers has one of an independentanode contact and a common anode contact and each one of the pluralityof lasers has one of an independent cathode contact and a common cathodecontact.